January Jones

The actress gave birth to son Xander Dane Jones in September 2011 and has yet to reveal the identity of his father. She previously said of the situation, "I knew I would be raising my son alone. It was something I went into knowingly, I was prepared mentally — and I was excited about it.”

Lena Headey

The Game of Thrones star gave birth to her second child, a girl, in July 2015, and it remains unclear who the father is. Some fans have assumed the dad is Lena's ex-husband, Peter Loughran, though the duo divorced in 2013. Her GoT co-star, Pedro Pascal, was also rumored to be the father.

Minnie Driver

The Oscar nominee welcomed son Henry in September 2008, and kept his father's identity secret for three years. It was later revealed that TV producer Timothy J. Lea, who worked with Minnie on The Riches, is the dad. "I don't need to protect him anymore," the actress said in 2012. "He can fend for himself. He's a grown-up. We weren't together and he wasn't directly in the business so I chose to protect him and not have a rain of publicity."

Geri Halliwell

The former Spice Girl had daughter Bluebell Madonna in May 2006, but kept her father off the birth certificate. It has since been revealed that screenwriter Sacha Gervasi is the dad. The duo reportedly had a six-week fling in 2005.